In an existing high-voltage inversion technology, a high-voltage converter, which is based on a direct serial connection of power electronic components, has a high requirement for dynamic and static equalizer circuits, and also has a high proportion of high-order harmonics in its output voltage, which makes it necessary to set an output filter. The proposition of a multi-level inverter circuit is a breakthrough progress for solving the above-mentioned problem. In a general structure of a multi-level inverter, typically, several level steps are combined into a step wave to approximate a sinusoidal output voltage. Due to the increased number of levels of the output voltage, the inverter reduces the proportion of harmonics in an output waveform and diminishes a voltage stress on a switch, so that an equalizer circuit is unneeded. For example, a switching tube is used to aid a neutral-point-clamped three-level inverter circuit, a diode clamped inverter circuit and a multi-level inverter which is mainly applied to such fields as speed control of a high-voltage high-power motor, reactive compensation, and active filtering.
Based on the three-level inverter circuit, more output levels can be implemented by adding more power semiconductors or by connecting low-level topologies in series. However, because the control logic of the inverter circuit in the solution is complicated, the solution is hard to implement.